Field of the Invention
The present invention relates to a stacking apparatus for stacking discharged sheets.
Description of the Related Art
In an apparatus for discharging a large-sized sheet as an output, such as a large-sized inkjet printer, the outputs may be accommodated in a container such as a basket. However, continuously discharging a plurality of the sheets into such a basket may cause the outputs to collide with each other every time a new sheet is discharged, possibly resulting in occurrence of damage, buckling and/or the like. Further, in the structure of printing an image on a continuous sheet held in a roll form before cutting the continuous sheet in accordance with the image, the cut sheet remains curled, making it difficult to stack and keep hold of a large number of sheets in the basket. Then, in recent years, a stacking apparatus (stacker) is provided to orderly stack sheets discharged from an apparatus for handling large-sized sheets.
Most of stacking apparatuses are structured such that a stacking tray for holding the discharged sheets is placed in a position downward in the gravity direction from the discharge port of a discharging apparatus and the discharged sheets respectively drop in order due to each own weight of the sheets to be stacked thereon. However, in a case of conveying and stacking strongly curled sheets, the leading end of the sheet during the discharge possibly abuts at a large angle on a stacking surface of the stacking tray to cause a conveyance failure of the sheet.
For solving this problem, Japanese Patent Laid-Open No. 2003-182915 discloses a supplementary tray which can be taken in and out for guiding and supporting sheets from the discharge port to the stacking tray. According to Japanese Patent Laid-Open No. 2003-182915, at the time when the leading end of the sheet passes through, the supplementary tray projects to cover a level difference gap between the discharge port and the stacking surface, and guides the sheet from the discharge port to the stacking surface while supporting it. On the other hand, at the time when the rear end of the sheet passes through, the supplementary tray retracts to expose the level difference gap between the discharge port and the stacking tray and cause the sheet rear end to drop to a predetermined position of the stacking surface.
In a case where the sheet already stacked on the stacking tray remains curled in a convex shape due to the curl, when the leading end of the incoming sheet newly discharged comes in contact with the mid-slope of convex the curl and moves forward, the sheet already stacked on the stacking tray is possibly pushed out of the stacking tray. To address this, for example, Japanese Patent Laid-Open No. 2003-261255 discloses the structure in which a concave configuration is provided on the stacking tray in a position in which the rear end of the sheet should be aligned and the rear end of the sheet curled in the convex shape is caused to enter into the concave configuration. When the rear end of the sheet enters into the concave configuration, even if the mid-slope of the sheet is pushed in the conveyance direction by the incoming sheet newly discharged, the travel of the sheet can be restricted, resulting in the aligning stacking of the sheets.
However, according to the structure disclosed in Japanese Patent Laid-Open No. 2003-182915, the supplementary tray does not project enough to contact with the stacking tray or the already stacked top sheet. Therefore the level difference gap still exists to some extent between the supplementary tray and the stacking tray. Further, even if the posture of the supplementary tray is designed to be adjusted in accordance with the amount of the stacked sheets such that this level difference gap is made sufficiently small, when a sheet of a large width is discharged in a state where a sheet of a small width is stacked thereon, a large level difference gap exists in a region where the sheet of the small width is not stacked. As a result, when the largely curled sheet is conveyed, the leading end enters into the level difference gap, possibly making normal conveyance impossible.
As in the case of Japanese Patent Laid-Open No. 2003-261255, in the structure provided with the concave portion for restricting the rear ends of the already stacked sheets, when the sheet number of the stacked sheets becomes large (for example, 100 sheets or more), the rear end of the top sheet cannot be sufficiently subjected to the restriction by the concave portion. Therefore when the leading end of the incoming sheet newly discharged comes in contact with the mid-slope of the stacked curled sheet and moves forward, the stacked sheet is moved to destroy the stacking state.